This invention relates to the preparation of a nickel/cobalt oxide impregnated nickel plaque material.
Mixed oxides are receiving considerable attention as catalysts both for oxygen reduction (fuel cells and metal/air batteries) and oxygen evolution (electrolytes). The problem is to prepare these catalysts inexpensively and to incorporate them into practical electrode structures. One mixed oxide of particular interest is nickel/cobalt spinel of the formula NiCo.sub.2 O.sub.4.
British Pat. No. 1,461,764 Published Jan. 19, 1977 to Walter J. King et al, discloses methods for the preparation of nickel/cobalt spinel which include the co-precipitation of nickel oxalate and cobalt oxalate followed by a heat treatment or freeze drying of the nitrates of nickel/cobalt followed by decomposition in vacuo and a heat treatment. The heat treatment is effected at about 400.degree. C. for 10 hours. These catalyst powders so formed are then mixed with carbon, for increased electrical conductivity, and a polytetrafluoroethylene binder and pressed onto a metal screen which acts as a current conductor. This method is quite complex. The freeze drying of the nitrates is advantageous from the point of view of high catalytic activity but is a very time consuming and costly procedure.
In Canadian Pat. No. 834,890, which issued on Feb. 17, 1970 to John H. Sizer et al, a method for the preparation of a nickel/cobalt oxide impregnated nickel plaque material is described. In the disclosed method, a layer of nickel oxide is formed on the plaque in a first oxidation step by heat treatment at 650.degree. C. The oxidized material is then impregnated with cobalt nitrate and a second oxidation step is performed at 500.degree. C. to form cobalt oxide and to react the cobalt oxide so formed with the already present nickel oxide, to form the nickel/cobalt spinel. This procedure is also time consuming and complex because of the multiple oxidation steps.
Both of the aforementioned patents involve heat treatments at 400.degree. to 650.degree. C. Applicant has found that heat treatments at such high temperatures have deleterious effects as well be apparent hereinafter.